Remove example project

[pdelboca]

fixes #328

I'm also renaming APP_EXAMPLE to APP_TMP to make more explicit that it is only a temporary folder.

How to test

1. Build the application
2. Install it
3. Open the application (by executing the application, not by running make start)
   a. Note: make start points the project folder of the application to another folder names ./tmp/project
4. Clean or backup your /home/<user>/.opendataeditor folder.
5. On first time run there shouldn't be any example files loaded.
6. The default project should point to /home/<user>/.opendataeditor/tmp

[cloudflare-pages]

Deploying opendataeditor with    Cloudflare Pages

Latest commit:	46d23b5
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Branch Preview URL:	https://328-remove-example-project.opendataeditor.pages.dev

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[guergana]

Reproduced following the steps in ubuntu and I can attest that it's working as expeted. ✔️ 💯